Fibers having improved sinusoidal configuration, concrete reinforced therewith and related method

Abstract

Fiber additives for addition to proportioned concrete comprise a plurality of thermoplastic fibers having a profile geometry defined by the equation, ##EQU1## wherein the amplitude a 0 falls within a range of from about 0.1 d f to 2.0 d f and the period λ falls within a range of from about 2 d f to 15 d f for fibers having a diameter d f of from about 0.5 to about 1 mm; the peak pull-out stress σ peak and the specific pull-out energy absorbed to a maximal displacement of 7.5 mm ψ peak , both increase linearly with a deformity factor defined by the equation, ##EQU2## where α=0.8 and β=-1, such that the peak pull-out stress is defined by the equation, ##EQU3## and the specific pull-out energy is defined by the equation, ##EQU4## the fiber additives having an optimimum deformity, D.sub.optimum ≈(0.5 to 1)D.sub.critical, D critical being that deformity where the ultimate tensile strength of the fiber equals k 1 D critical +C, and where loads are measured in N; energy in N-mm; length dimensions are in mm, and the values of k 1 , k 2 , C and C 1 are determined based upon the ultimate tensile strength of the fiber and by plotting deformation versus pull-out stress to obtain the value for D critical . The present invention also provides concrete having improved crack resistance and a method for improving the bond slip performance of fibers in concrete utilizing the sinusoidally configured fibers of the present invention.

What is claimed is: 
     
       1. Fiber additives for addition to concrete comprising: a plurality of thermoplastic fibers having a profile geometry defined by the equation, ##EQU23## wherein the amplitude a 0  falls within a range of from about 0.1 d f  to 2 d f  and the period λ falls within a range of from about 2 d f  to 15 d f  for fibers having a diameter d f  of from about 0.5 to about 1 mm; the peak pull-out stress σ peak  and the specific pull-out energy absorbed to a maximal displacement of 7.5 mm ψ peak , for said fibers, when embedded in concrete, both increase linearly with a deformity factor defined by the equation, ##EQU24## where α=0.8 and β=-1, such that the peak pull-out stress is defined by the equation, ##EQU25## and the specific pull-out energy is defined by the equation, ##EQU26## said fiber additives having an optimum deformity,   D.sub.optimum ≈(0.5 to 1)D.sub.critical,     D critical  being that deformity where the ultimate tensile strength of the fiber equals k 1  D critical  +C, and where loads are measured in N; energy in N-mm; length dimensions are in mm, and the values of k 1 , k 2 , C and C 1  are determined based upon the ultimate tensile strength of the fiber and by plotting deformation versus pull-out stress to obtain the value for D critical .     
     
     
       2. Fiber additives, as in claim 1, wherein said plurality of fibers are selected from the group consisting of polyolefins; polyesters; polyvinyl chloride; polyvinylidene chloride; polyamides; polyacrylics and mixtures thereof. 
     
     
       3. Fiber additives, as in claim 1, wherein said plurality of fibers are polypropylene, having an ultimate tensile strengh of 450 MPa and where k 1  =2300; k 2  =12300; C=27.5 and, C 1  =186. 
     
     
       4. Fiber additives, as in claim 1, wherein said plurality of fibers have a diameter of from 0.6 to about 0.8 mm, an amplitude of from 0.5 d f  to about 1 d f  and a period of from 4 d f  to about 7 d f . 
     
     
       5. Fiber additives, as in claim 1, wherein said plurality of fibers have a diameter of 0.76 mm, an amplitude of 0.52 mm and a period of 3.9 mm. 
     
     
       6. Concrete having improved crack resistance comprising: concrete; and   from about 0.25 to about 5 percent by volume of sinusoidally configured thermoplastic fibers having a profile geometry defined by the equation, ##EQU27## wherein the amplitude a 0  falls within a range of from about 0.1 d f  to 2 d f  and the period λ falls within a range of from about 2 d f  to 15 d f  for fibers having a diameter d f  of from about 0.5 to about 1 mm; the peak pull-out stress σ peak  and the specific pull-out energy absorbed to a maximal displacement of 7.5 mm ψ peak , both increase linearly with a deformity factor defined by the equation, ##EQU28## where α=0.8 and β=-1, such that the peak pull-out stress is defined by the equation, ##EQU29## and the specific pull-out energy is defined by the equation, ##EQU30## said fiber additives having an optimum deformity,   D.sub.optimum ≈(0.5 to 1)D.sub.critical,     D critical  being that deformity where the ultimate tensile strength of the fiber equals k 1  D critical  +C, and where loads are measured in N; energy in N-mm; length dimensions are in mm, and the values of k 1 , k 2 , C and C 1  are determined based upon the ultimate tensile strength of the fiber and by plotting deformation versus pull-out stress to obtain the value for D critical .     
     
     
       7. Concrete, as in claim 6, wherein said plurality of fibers are selected from the group consisting of polyolefins; polyesters; polyvinyl chloride; polyvinylidene chloride; polyamides; polyacrylics and mixtures thereof. 
     
     
       8. Concrete, as in claim 7, wherein said plurality of fibers comprise polypropylene having an ultimate tensile strengh of 450 MPa and where k 1  =2300; k 2  =12300; C=27.5 and, C 1  =186. 
     
     
       9. Concrete, as in claim 6, wherein said plurality of fibers have a diameter of from 0.6 to about 0.8 mm, an amplitude of from 0.5 d f  to about 1 d f  and a period of from 4 d f  to about 7 d f . 
     
     
       10. Concrete, as in claim 6, wherein said plurality of fibers have a diameter of 0.76 mm, an amplitude of 0.52 mm and a period of 3.9 mm. 
     
     
       11. A method for improving the bond slip performance of fibers in concrete comprising the steps of: adding to a selected amount of concrete, from about 0.25 to about 5 percent by volume, of sinusoidally configured thermoplastic fibers having a profile geometry defined by the equation, ##EQU31## wherein the amplitude a 0  falls within a range of from about 0.1 d f  to 2 d f  and the period λ falls within a range of from about 2 d f  to 15 d f  for fibers having a diameter d f  of from about 0.5 to about 1 mm; the peak pull-out stress σ peak  and the specific pull-out energy absorbed to a maximal displacement of 7.5 mm ψ peak , both increase linearly with a deformity factor defined by the equation, ##EQU32## where α=0.8 and β=-1, such that the peak pull-out stress is defined by the equation, ##EQU33## and the specific pull-out energy is defined by the equation, ##EQU34## said fiber additives having an optimum deformity,   D.sub.optimum ≈(0.5 to 1)D.sub.critical,     D critical  being that deformity where the ultimate tensile strength of the fiber equals k 1  D critical  +C, and where loads are measured in N; energy in N-mm; length dimensions are in mm, and the values of k 1 , k 2 , C and C 1  are determined based upon the ultimate tensile strength of the fiber and by plotting deformation versus pull-out stress to obtain the value for D critical  ; and     mixing said components sufficiently to distribute said fibers uniformly throughout said concrete, whereby energy absorption capability of concrete is improved as compared to concrete reinforced by fibers having a geometry other than said geometry.   
     
     
       12. A method, as in claim 11, wherein said pluralities of fibers are selected from the group consisting of polyolefins; polyesters; polyvinyl chloride; polyvinylidene chloride; polyamides; polyacrylics and mixtures thereof. 
     
     
       13. A method, as in claim 12, wherein said plurality of fibers are polypropylene having an ultimate tensile strengh of 450 MPa and where k 1  =2300; k 2  =12300; C=27.5 and, C 1  =186. 
     
     
       14. A method, as in claim 11, wherein said plurality of fibers have a diameter of from 0.6 to about 0.8 mm, an amplitude of from 0.5 d f  to about 1 d f  and a period of from 4 d f  to about 7 d f . 
     
     
       15. A method, as in claim 11, wherein said plurality of fibers have a diameter of 0.76 mm, an amplitude of 0.52 mm and a period of 3.9 mm.